Immunochromatography is a known example of an immunoassay method that detects a specific substance to be detected using an antigen-antibody or other specific reaction.
Immunochromatography is a testing method widely used as a Point Of Care Test (POCT). POCT are performed near the patient instead of sending the patient's specimen to a testing facility so as to enable the physician to rapidly assess the test results and promptly initiate treatment. Immunochromatography is used to diagnose infections derived from bacteria and viruses, and particularly infections in cases involving newborns or the elderly having diminished immune strength that require immediate treatment, and is required to demonstrate rapid and highly sensitive detection.
Simple test kits are used for assays based on immunochromatography (see PTL 1). Test kits are kits that consist of (1) allowing a liquid sample to develop downstream by capillary phenomenon, and (2) detecting a substance to be detected in the sample. Whether or not the substance to be detected is contained in the liquid sample is determined by whether or not a test line provided downstream of the liquid in the direction of development is labeled.
FIG. 9 is a side view of a test kit of the prior art that uses immunochromatography. A test kit a has a kit body b, which detects a substance to be detected by developing a liquid sample, an absorbent pad c, which takes up the liquid sample downstream of the kit body b, and a sheet d on which the kit body b and the absorbent pad c are installed. The kit body b has a plurality of members, and more specifically, a liquid dropping pad e, a labeling substance holding pad f and an immobilizing membrane g. At least some of these members e through g are mutually connected to allow development of the liquid sample. The following provides an explanation of each member of the kit body b.
The sample dropping pad e is a pad for dropping the liquid sample.
The labeling substance holding pad f is a pad in which the labeling substance is uniformly held. The labeling substance holding pad f is fabricated by impregnating a pad with a solution containing the labeling substance, followed by drying. Furthermore, the labeling substance referred to here refers to a substance in which a first substance (antibody or antigen), which specifically binds with a substance to be detected (antigen or antibody) in the liquid sample, is immobilized on insoluble carrier particles, an enzyme-labeled ligand or a fluorescence-labeled ligand serving as a label.
The immobilizing membrane g is a pad on which a second substance (antibody or antigen), which specifically binds with a substance to be detected in the liquid sample, is immobilized in the form of a line.
The following indicates typical behavior within the test kit a when using the above-mentioned test kit a.
When a liquid sample is dropped onto the sample dropping pad e, the liquid sample develops through the liquid dropping pad e and flows into the labeling substance holding pad f through an interface h with the labeling substance holding pad f. Then, the labeling substance uniformly held in the labeling substance holding pad f is made to flow out by the liquid sample and flow into the immobilizing membrane g together with the liquid sample through an interface i with the immobilizing membrane g. Moreover, the liquid sample develops through the immobilizing membrane g and is absorbed by the absorbent pad c through an interface j with the absorbent pad c.
As described above, in the case a substance to be detected is contained in the liquid sample, the substance to be detected binds with the first substance of the labeling substance. The second substance immobilized in the form of a line on the immobilizing membrane g becomes an immobilized sample, and the substance to be detected having a labeling substance bound thereto binds therewith and is captured in the form of line. As a result, since the labeling substance is captured in the form of a line, it can be confirmed by viewing the labeled test line and the substance to be detected in the sample is detected.